arangosh> db.test.ensureIndex({ type: "hash", fields: [ "a" ], sparse: true }); { "deduplicate" : true, "fields" : [ "a" ], "id" : "test/110314", "isNewlyCreated" : true, "selectivityEstimate" : 1, "sparse" : true, "type" : "hash", "unique" : false, "code" : 201 } arangosh> db.test.ensureIndex({ type: "hash", fields: [ "a", "b" ], unique: true }); { "deduplicate" : true, "fields" : [ "a", "b" ], "id" : "test/110317", "isNewlyCreated" : true, "selectivityEstimate" : 1, "sparse" : false, "type" : "hash", "unique" : true, "code" : 201 }